A human heart receives its blood supply from the coronary arteries, which branch out and around the heart muscle. Conversely, in a reptile, little or no arterial supply of blood is provided to the heart. Instead, the blood supply is mainly delivered into the heart muscle from the inside surface of the heart chamber.
Modifying a human heart to imitate the blood delivery method of a reptile heart is currently being used as an alternative or adjunct to both coronary artery bypass graft surgery and coronary balloon angioplasty. Normally, a person can only undergo coronary bypass surgery twice, since the risks will begin to outweigh the benefits after that point. Thus, in the past, a patient who has already had two coronary bypass surgeries was left with no recourse. Others have failed repeated coronary balloon angioplasties, and many persons are not suitable candidates for coronary bypass surgery or coronary balloon angioplasty. These persons likewise are left with no treatment options.
Early attempts to imitate the reptilian condition in mammals, known as transmyocardial revascularization (TMR), consisted of producing tiny channels in mammalian and human hearts with needles or pre-heated wires. These methods met with limited success since, although the channels closed by clotting at the outside surface of the heart due to exposure to air, and did allow for some internal blood delivery, the channels soon healed over entirely and failed to continue to enhance the blood supply. Early attempts were also made to graft a blood vessel from the aorta directly into the heart muscle to provide an internal source of blood. While some benefits were seen, the surgery was technically demanding and the procedure was eclipsed by the introduction of coronary artery bypass graft surgery.
To overcome these problems, Mahmood Mirhoseini and Mary M. Cayton attempted transmyocardial revascularization by using a CO.sub.2 laser to make the channels. Mirhoseini M., Cayton M. M., Revascularization of the Heart by Laser, J Microsurg 2:253, June, 1981. The laser forms each channel by vaporizing a passageway completely through the wall of the heart. The relatively clean channel formed by the laser energy prevents the channel from healing over, and the channel either closes by clotting at the heart's outer surface, due to exposure to air, or manual pressure can be applied until bleeding from the channel ceases. In some cases, a suture is required to close the channel. However, if bleeding cannot be stopped, or if bleeding resumes at a later time, after the patient is no longer in surgery, the patient may require emergency surgery or may die.
Generally, it is desired that the channels be made primarily within the heart's inner surface (endocardium) since the endocardium has a greater need of an alternative supply of blood than the heart's outer surface (epicardium). It would be desirable not to create too large a channel through the epicardium because the channel must clot and/or heal at the heart's surface to prevent copious blood loss due to the forceful pumping action of the heart. It would be desirable to produce a channel which is very small in the epicardium, so that clotting can easily close the channel at the heart's outer surface, as well as a channel which is widest at the point the channel exits the inner surface of the heart chamber, thus admitting a larger volume of blood and being less susceptible to clotting or healing.
The present invention satisfies these objectives by providing an improved device and procedure that employs radio-frequency electrical energy to form a channel.